Keywords

1 Introduction

The demand for innovative wireless communication applications is drastically increasing day by day [1, 2]. To fulfill this demand, there is a necessity for novel and optimized communication devices like reconfigurable antennas, phase shifters, and RF isolators with low power consumption. Especially in 5G technology, there is a significant demand for reconfigurable antennas with multi-operating frequencies and low interferences [3, 4]. The researchers are investigated with intense curiosity to propose the optimized solution and to design a reconfigurable antenna with best performance. In this era, MEMS technology is shown great potential in the design of communication devices with low power consumption and high linearity.

This is the major motivated factor to design reconfigurable antennas by using RF MEMS switches other than traditional solid-state electronic switches (PIN diode and FET transistor) [5,6,7]. MEMS technology has recently received significant attention due to its ability to enhance the performance of RF switches. Despite the best performance, decreasing the pull-in voltage, increasing the reliability, and improving the switching time are significant research challenges in RF MEMS switches. Improving the capacitance ratio and achieving the best RF performance are the potential challenges in capacitive RF MEMS switches [8,9,10]. RF MEMS switch-based reconfigurable antennas are offering the best performance when compared with structure-based reconfigurable antennas [11,12,13].

In this paper, we have presented an investigation and design analysis on the performance of reconfigurable antennas using shunt capacitive RF MEMS switches. These configurations aim to provide the following bands: GPS bands (1.2–1.6 GHz), WLAN bands (2.39–2.4 and 5.2–5.6 GHz), RFID (0.9–5.2 GHz), some satellite bands (3.7–4.2, 5.1–6.25, and 6.7–7.1 GHz), and GSM bands (1.85–1.9 GHz) (Table 1).

Table 1 Wireless applications based on frequency bands [14,15,16]
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2 Reconfigurable Antenna

In this paper, we have designed a reconfigurable microstrip patch antenna using shunt capacitive RF MEMS switches. The antenna is aimed to serve multiple applications like RFID, WLAN, GPS, and WiMAX applications.

2.1 RF MEMS Switches

The shunt capacitive RF MEMS switches are used as the basic switching elements used for making the antenna as reconfigurable. The switch is designed with serpentine structure membrane of gold (Au) material of 1 µm thickness (Table 2; Figs. 1, 2 and 3).

Table 2 RF MEMS switch materials and dimensions
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Fig. 1
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Serpentine membrane electrostatic actuation

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Fig. 2
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Actuation voltage (Vs) displacement

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Fig. 3
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Serpentine membrane resonant frequencies, a 4608 Hz, b 7772 Hz, 12244 Hz

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The membrane is perforated with 5 µm × 5 µm size square shape holes. Electrostatic actuation is used to deform the membrane. The RF MEMS switch designed using COMSOL tool is offering good performance i.e., the required actuation voltage is 4.5 V, the switching time of the switch is 45 µs. We have done a wide range of analyses on the serpentine membrane in terms of max/min actuation voltages points, max/min displacement points, isolating surface for electric potential, displacement direction, and contour for electric potential, principal stress points.

2.2 Reconfigurable Antenna Using RF MEMS Switches

The reconfigurable microstrip patch antenna is designed by placing three identical shunt capacitive RF MEMS switches i.e., S1, S2, and S3 (Fig. 4).

Fig. 4
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Reconfigurable antenna with three identical RF MEMS switches, a top view, b side view

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All three switches are individually connected to biasing pads. Silicon is used as a substrate. Silicon dioxide is used as an insulating material on the top of the silicon substrate (Figs. 5 and 6).

Fig. 5
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Flow of current

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Fig. 6
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Reconfigurable antenna resonating at multiple frequencies under different switching conditions

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CPW type feeding is used with G/S/G value 50 µm/100 µm/50 µm. The structure of the reconfigurable antenna is designed by connecting the four patches i.e., P1, P2, P3, and P4. The P1 patch is conned with P2, P3, and P4 through three switches S1, S2, and S3, respectively. If S1-OFF, S2-OFF, and S3-OFF, the antenna is resonating at 5.4 GHz. If S1-OFF, S2-OFF, and S3-ON, the antenna is resonating at 0.9 GHz. If S1-OFF, S2-ON, and S3-ON, the antenna is resonating at 1.5 GHz. If S1-OFF, S2-ON, and S3-ON, the antenna is resonating at 3.5 and 8.4 GHz. Based on the switching of the RF MEMS switches, the antenna is resonating at 0.9, 1.5, 3.5, and 5.4 GHz. So, the proposed antenna is suitable for multiple applications like RFID, GPS, WiMAX, and WLAN (Table 3).

Table 3 Antenna resonating frequencies under different switching conditions
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3 Conclusion

The demand for the reconfigurable antenna is increasing day by day. In this paper, we have designed a reconfigurable microstrip patch antenna for low-frequency communication applications using shunt capacitive RF MEMS switches. The RF MEMS switch used is offering high performance. The reconfigurable antenna is designed with three RF MEMS switches. Based on the switching of the RF MEMS switches, the antenna is resonating at 0.9, 1.5, 3.5, 5.4 GHz. So, the designed antenna is suitable for multiple applications like RFID, GPS, WiMAX, and WLAN.